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| 3. |
- Alcocer, Alex, et al.
(author)
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Force Estimation and Control in Robot Manipulators
- 2004
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In: Robot control 2003 : A proceeding volume from the 7th IFAC Symposium Wroclaw, Poland, 1-3 September 2003 - A proceeding volume from the 7th IFAC Symposium Wroclaw, Poland, 1-3 September 2003. - 0080440096 ; 1, s. 31-36
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Conference paper (peer-reviewed)abstract
- In this paper we present some results on model based force estimationand how these estimates can be integrated in a common robot force controlscheme. A generalization of the force estimation method proposed inHacksel and Salcudean (1994) is done and a force observerable to follow ramp environmental forces is introduced. Anextension of this method for robotic manipulators is also experimentallyverified for an industrial robot with an open control systemarchitecture during a force control task.
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| 4. |
- Amani, Payam, et al.
(author)
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Application of Control Theory to a Commercial Mobile Service Support System
- 2012
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In: International Journal on Advances in Telecommunications. - 1942-2601. ; 5:3&4
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Journal article (peer-reviewed)abstract
- The Mobile Service Support system (MSS), which Ericsson AB develops, handles the setup of new subscribers and services into a mobile network. Experience from deployed systems show that traffic monitoring and control of the system will be crucial for handling overload situations that may occur at sudden traffic surges. In this paper we identify and explore some important control challenges for this type of systems. Further, we present analysis and experiments showing some advantages of proposed solutions. First, we develop a load-dependent server model for the system, which is validated in testbed experiments. Further, we propose a control design based on the model, and a method for estimation of response times and arrival rates. The main contribution of this paper is that we show how control theory methods and analysis can be used for commercial telecom systems. Parts of our results have been implemented in commercial products, validating the strength of our work.
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| 5. |
- Amani, Payam, et al.
(author)
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Multi-step ahead response time prediction for single server queuing systems
- 2011
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In: [Host publication title missing].
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Conference paper (peer-reviewed)abstract
- Multi-step ahead response time prediction of CPU constrained computing systems is vital for admission control, overload protection and optimization of resource allocation in these systems. CPU constrained computing systems such as web servers can be modeled as single server queuing systems. These systems are stochastic and nonlinear. Thus, a well-designed nonlinear prediction scheme would be able to represent the dynamics of such a system much better than a linear scheme. A nonlinear autoregressive neural network with exogenous inputs based multi-step ahead response time predictor has been developed. The proposed estimator has many promising characteristics that make it a viable candidate for being implemented in admission control products for computing systems. It has a simple structure, is nonlinear, supports multi-step ahead prediction, and works very well under time variant and non-stationary scenarios such as single server queuing systems under time varying mean arrival rate. Performance of the proposed predictor is evaluated through simulation. Simulations show that the proposed predictor is able to predict the response times of single server queuing systems in multi-step ahead with very good precision represented by very small mean absolute and mean squared prediction errors.
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| 6. |
- Amani, Payam, et al.
(author)
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NARX-based multi-step ahead response time prediction for database servers
- 2011
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In: [Host publication title missing]. - 2164-7143. - 9781457716768 ; , s. 813-818
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Conference paper (peer-reviewed)abstract
- Advanced telecommunication applications are often based on a multi-tier architecture, with application servers and database servers. With a rapidly increasing development of cloud computing and data centers, characterizations of the dynamics for database servers during changing workloads will be a key factor for analysis and performance improvements in these applications. We propose a multi-step ahead response time predictor for database queries based on a nonlinear autoregressive neural network model with exogenous inputs. The estimator shows many promising characteristics which make it a viable candidate for being implemented in admission control products for database servers. Performance of the proposed predictor is evaluated through experiments on a lab setup with a MySQL-server.
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| 7. |
- Andersson, Alina, et al.
(author)
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Analytic Parameterization of Stabilizing Controllers for the Surge Subsystem of the Moore-Greitzer Compressor Model
- 2013
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In: Proc. 2013 American Control Conference (ACC2013). - 0743-1619. - 9781479901777 ; , s. 5257-5262
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Conference paper (peer-reviewed)abstract
- This paper is based on a new procedure for dynamic output feedback design for systems with nonlinearities satisfying quadratic constraints. The new procedure is motivated by the challenges of output feedback control design for the 3-state Moore-Greitzer compressor model. First, we use conditions for stability of a transformed system and the associated matching conditions to find the data of the stabilizing controllers for the surge subsystem. Second, using the set of stabilizing controllers satisfying the given constraints for the closed-loop system with the dynamic output feedback controller we made optimization over the parameter set. We present the data of the stabilizing controllers and the new constraints for the corresponding parameters. The contributions in this paper are simplified conditions for the synthesis and optimization over the control parameter set.
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| 8. |
- Andersson, Alina, et al.
(author)
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Robustness of the Moore-Greitzer Compressor Model's Surge Subsystem with New Dynamic Output Feedback Controllers
- 2014. - 3
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In: 19th IFAC World Congress. - : Elsevier. - 2405-8963. - 9783902823625 ; 47, s. 3690-3695
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Conference paper (peer-reviewed)abstract
- This work presents an extension of a design procedure for dynamic output feedback design for systems with nonlinearities satisfying quadratic constraints. In this work we used an axial gas compressor model described by the 3-state Moore-Greitzer compressor model (MG) that has some challenges for output feedback control design (Planovsky and Nikolaev 1990), (Rubanova 2013). The more general constraints for the investigation of the robustness with respect to parametric uncertainties and measurement noise are shown.
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| 9. |
- Andersson, Alina, et al.
(author)
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Sufficient Conditions for Dynamic Stabilization of 3-State Moore-Greitzer Compressor Model
- 2015
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In: 2015 IEEE 54th Annual Conference on Decision and Control (CDC). - 9781479978861 - 9781479978847 ; , s. 4394-4399
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Conference paper (peer-reviewed)abstract
- We consider the classical 3-state Moore-Greitzer model, which is commonly used for approximating dynamics of deviations of flow and pressure variables in an axial compressor from their nominal steady-state values. The linearization of the nonlinear system is not controllable and, therefore, even local asymptotic stability cannot be achieved using methods of linear control theory. We propose a family of parametrized partialstate feedback control laws and derive sufficient conditions to guarantee global asymptotic stability of the closed-loop system. The stability analysis uses the integral quadratic constraints technique for the case of non-strict frequency condition and novel arguments for characterization of omega-limit sets.
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| 10. |
- Andersson, Mikael, et al.
(author)
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Admission control of the Apache web server
- 2004
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In: Seventeenth Nordic Teletraffic Seminar, NTS 17, Fornebu, Norway, 25-27 August 2004. - 8242305951
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Conference paper (peer-reviewed)abstract
- Web sites are exposed to high rates of incoming requests. The servers may become overloaded during temporary traffic peaks when more requests arrive than the server is designed for. An admission control mechanism rejects some requests whenever the arriving traffic is too high and thereby maintains an acceptable load in the system. This paper presents how admission control mechanisms can be designed with a combination of queueing theory and control theory. In this paper we model an Apache web server as a G/G/1-system and then design a PI-controller, commonly used in automatic control, for the server. The controller has been implemented as a module inside the Apache source code. Measurements from the laboratory setup show how robust the implemented controller is, and how it correspond to the results from the theoretical analysis.
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